We live in the environment that comprises many kind of energies that flow out of the primary source in the use and may form a small flow as the main purpose of the energy used has been fulfilled, but there is still a residual or a secondary energy that has been still in the system present in a damped level or in another form.
Tire pressure measurement systems in automotive tires are common today. In a typical state of the art system a pressure and temperature sensor module is combined with a radio transmitter and assembled on the valve stem inside the tire. The electrical energy for the module is supplied by a battery. The energy available from the battery limits the signal transmission frequency and operating life of the module. The transmission frequency can be as low as once per minute. Also motion switches are in use to enable the transmission only when the tire is rotating at sufficiently high speed.
Alternative solutions have been proposed for the energy source. One solution is to supply the electrical energy to the module via electromagnetic fields. High frequency radio signals have been used as well as low frequency magnetic field coupling. Enough energy can be transmitted for update frequency up to once per second. Also no motion switch is needed. The disadvantage is the need for an antenna and associated cables in the vicinity of each tire. This has rendered the system too costly for practical implementation.
A third alternative state of the art solution is to generate the electrical energy from available mechanical, thermal, radiation or similar energy sources that may be present in the tire. A reliable source of mechanical energy is provided by the rotary motion of the tire. A great amount of energy is available as mechanical power compared to the 10 . . . 100 μW electrical power needed.
Also it is desirable to mount the measurement module on the inner liner of the tire since at this location a representative temperature reading can be obtained, not influenced by the brakes. Also, if the measurement module is combined with the tire and not the valve or rim, tire parameter information can be transmitted in addition to pressure and temperature readings.
However, if considering the connections to external energy sources, they are difficult to reliably implement, in a closed systems as tires. External energy sources have to be replaced and/or loaded to restore the functionality of the in-tire-system electronics, such as the measurement electronics and/or transmitters to collect, save and/or report wirelessly the measurement results. In such conditions of the system where external energy sources are—if not entirely impossible—but at least very difficult to apply, the internal energy source is wanted.
However, although energy is surrounding ourselves in the world in many ways, the utilization of such loose energy, which is sometimes referred as degenerated energy, is problematic, especially in such a closed system as rotatable tire interior. The amount of such energy is sufficient for many purposes of digital electronics, but the implementation for mining of the energy and/or the conversion the available energy to utilizable form has not been yet found, except very low-level energy yields to be gained according to the known techniques as such, so that the electronics involved in the tire structure may be not operable reliably.